Laws governing who can observe voters at the polls and what those observers can do vary from state to state. Some questions and answers about what is and is not allowed on Election Day:

WHO CAN OBSERVE?

States have a variety of rules about who can monitor polling places, but observers generally fall into three categories: partisan, nonpartisan and international.

Partisan observers are appointed by political parties or candidates and usually are required to sign up in advance to monitor polling places. Nearly every state allows partisan observers, and most of them specify how many can be present at each polling place and what they can or cannot do while there. In Pennsylvania, for example, official poll watchers must live in the county where they monitor elections, a rule that the Republican Party is challenging in federal court.

Nonpartisan or citizen observers also are common at polling places and are permitted by at least 35 states and the District of Columbia, according to research by the National Conference of State Legislatures. Most of those states lack specific legislation regulating nonpartisan observers but allow them in practice.

International observers are allowed in at least 33 states and the District of Columbia, according to the NCSL. These observers usually are deployed by international nonpartisan groups with the goal of promoting free, democratic elections and respect for human rights. They are bound by a code of conduct. The U.S. committed to allowing international observers when it signed an agreement with the Organization for Security and Cooperation in Europe in 1990, and the group began sending observers to the U.S. in 2002. This year, it plans to send more than 400 observers, a nearly tenfold increase over the last presidential election four years ago.

WHAT IF OBSERVERS HAVE AN AGENDA?

States do not have specific rules regarding election observers who, while not explicitly partisan, have a stake in the outcome of the race. In practice, such poll watchers are generally treated as nonpartisan or citizen observers, even though they may have a partisan agenda.

Donald Trump has urged his supporters to show up at polling places and look out for possible voter fraud. Right-wing groups including the Oath Keepers, a coalition of former police officers and members of the military, are urging members to do the same. Meanwhile, civil rights groups are asking poll watchers to look out for people being unfairly denied the right to vote, especially minorities who tend to vote Democratic.

CAN POLL WATCHERS CARRY GUNS?

The District of Columbia and 11 states have laws explicitly banning guns at polling places. In states that do not restrict the open carrying of handguns, poll watchers could legally be armed outside a polling location. However, nearly all states ban the carrying of firearms in schools and government buildings, where many polling places are located. That would preclude the possibility of armed citizens watching people as they cast ballots.

Arkansas used to be among the states that banned carrying concealed weapons into polling places. The ban was repealed last year, meaning that voters and poll watchers can legally be armed.

HOW CAN VOTERS BE CHALLENGED?

Thirty-nine states allow citizens to challenge the eligibility of their fellow voters inside polling places, and 28 allow the challenge to be issued before someone votes, according to a 2012 report by the Brennan Center for Justice at New York University School of Law. At least four battleground states – Florida, Iowa, Nevada and Pennsylvania – not only allow people to challenge voters inside polling places but place the burden of proof on the person who is challenged.

In recent years, Alabama, Ohio and Texas have banned citizen challenges at the polls. Other states allow only election officials to challenge voters.

WHAT CONSTITUTES VOTER INTIMIDATION?

Nearly every state has laws banning poll watchers from intimidating, harassing or threatening voters. Federal law prohibits voter intimidation on the basis of race, ethnicity or the language they speak. Poll watchers who seek to challenge a voter are generally prohibited from approaching voters themselves. Instead, they must file their challenge with on-site election workers.

The Republican National Committee is barred by a 1982 court order from monitoring polling places for fraud after Democrats sued over alleged voter intimidation in minority communities.

WHERE CAN VOTERS GET HELP?

Voting rights experts encourage anyone who encounters problems at the polls to stay calm and find out what needs to be done to have their ballot counted. Voters also can call the U.S. Department of Justice (800-253-3931) and the nonpartisan Election Protection coalition (866-OUR-VOTE).